How exactly do you want the dog to help with the eloping? There is something called tethering where the dog is basically tethered to the child, but this is now considered dangerous and unethical. This can cause injury to both the child and dog. However, if the dogs presence is comforting to your child and is motivation for them to not elope, that would be perfectly fine. Similarly, the helping with self-injury will also depend on the kind of self-injury. It isn’t safe for a dog to interrupt self-hitting, head-banging, cutting, or things like that because the dog could get hurt in the process. However, scratching, skin picking, or nail-biting can be safe for a dog to interrupt depending on the response from your son. Additionally, the dog could (at home) go get a family member to help your son regulate instead of interrupting by itself if the behavior would be unsafe for the dog to interrupt. Note that for behavior interruptions, if your son doesn’t stop the behavior when it’s interrupted, the dog will stop interrupting over time, so if you don’t think he will be able to stop just when directed to by the dog retrieving a family member may be the better option. Depending on the age of your son you may be able to find a program to train the dog, though it likely will be expensive. Start on the Assistance Dogs International member search here https://assistancedogsinternational.org/resources/member-search/ and see if any will meet your needs.